Mark Volpe, the orchestra’s managing director, said that Mr. Nelsons, 34, was struck in the head by a door that unexpectedly swung open at his house in Bayreuth, Germany, this past weekend. Mr. Nelsons was in Bayreuth to conduct at the Wagner festival.

“He went to a rehearsal,” Mr. Volpe said on Monday afternoon, “and quickly realized that the injury was more serious than he had at first thought. He went to a hospital, where they diagnosed a severe concussion. He’s still in the hospital, and will remain there for a few more days as they monitor him. The encouraging news is that he’s making progress, but no doctor will allow him to get on an airplane at this point.”

Mr. Nelsons was to have led a single performance of the Verdi Requiem in his only scheduled Tanglewood performance this summer. He was also set to meet informally with the music students at Tanglewood, attend a lunch with the board, and participate in an audience question-and-answer session. He conducts the Boston Symphony next in October, and is scheduled to return to Tanglewood for a longer stay next summer.

“I promise I will recover as soon as possible,” Mr. Nelsons said in a statement, “and very much look forward to coming back in good shape for my performances with the orchestra in October in Boston.”